This research proposal is interested in the mechanisms involved in human mammary carcinogenesis and its prevention. In murine systems the process of mammary cell transformation progresses via distinct steps of initiation, promotion and progression. The critical molecular and cellular events characterizing human mammary cell transformation have not been identified. Dietary interventions involving restriction of polyunsaturated omega-6 fatty acids, supplementation with saturated fatty acids and polyunsaturated omega-3 fatty acids or hyperalimentation with retinoids inhibit, retard or prevent murine mammary tumorigenesis. The efficacy of such dietary interventions to prevent human mammary cancer is yet to be validated. With comparative studies on the newly developed human mammary explant culture system and on the well-standardized murine mammary explant culture system the present proposal seeks to test the hypothesis that the process of mammary cell transformation progresses via similar molecular and cellular events in the two systems, and that the prototype modulators of murine mammary tumorigenesis can inhibit, retard or prevent the preneoplastic steps in human mammary cell transformation. The explant cultures will be exposed to the carcinogens, 7,12- dimethylbenz(a) anthracene (DMBA) and N-nitroso-N-methylurea (NMU). The in vitro response of the tissue to the carcinogens will be evaluated at the molecular level by measuring the induction of DNA damage/repair and 6-thioguanine and/or Ouabain resistant (TGr/OUr) mutants. The cellular response to the carcinogens will be assessed by determining the incidence of ductal or alveolar hyperplasia with atypia and by the morphogenetic and tumorigenic potential of the transplanted atypical lesions. In the cell cultures derived from the 'preneoplastic' lesions, the persistance of 'transformed' phenotype will be demonstrated by measuring the cell growth in calcium and/or serum depleted medium, persistance of TGr/OUr mutants, acquisition of anchorage-independent growth and formation of atypical epithelial hyperplasia and/or tumor at the transplant site. The modulatory influence of selected fatty acids and retinoids will be evaluated by measuring the alterations induced in the quantitative parameters detailed above. The proposal will provide a basis for future studies with focus in more detail on the mechanisms in human mammary carcinogenesis and its prevention.